Flight Trajectory Recreation And

8/13/2019 Flight Trajectory Recreation And

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David C. Wyld et al. (Eds) : CST, ITCS, JSE, SIP, ARIA, DMS - 2014

pp. 141154, 2014. CS & IT-CSCP 2014 DOI : 10.5121/csit.2014.4114

FLIGHTTRAJECTORYRECREATIONANDPLAYBACK SYSTEMOFAERIALMISSION

BASEDONOSSIMPLANET

Wu Wu1, Jiulin Hu

2, Xiaofang Huang

3, Huijie Chen

4,Bo Sun

5

College of Information Science and Technology,

Beijing Normal University, Beijing, [email protected]

ABSTRACT

Recreation of flight trajectory is important among research areas. The design of a flight

trajectory recreation and playback system is presented in this paper. Rather than transferringthe flight data to diagram, graph and table, flight data is visualized on the 3D global of

ossimPlanet. ossimPlanet is an open-source 3D global geo-spatial viewer and the system

realization is based on analysis it. Users are allowed to choose their interested flight of aerial

mission. The aerial photographs and corresponding configuration files in which flight data is

included would be read in. And the flight statuses would be stored. The flight trajectory is then

recreated. Users can view the photographs and flight trajectory marks on the correct positions

of 3D global. The scene along flight trajectory is also simulated at the planes eye point. This

paper provides a more intuitive way for recreation of flight trajectory. The cost is decreased

remarkably and security is ensured by secondary development on open-source platform.

KEYWORDS

flight trajectory,open-source platform,3D global, ossimPlanet, KML

1. INTRODUCTION

Flight trajectory is important in the flight collision, flight planning, flight accidents investigation

and flight simulation areas. Generally, the recreation of flight trajectory [1-2] is to transfer theflight data to the diagram, graph, table, etc. It is important in aircraft safety assessments, aircraft

maintenance, accident investigation and event analysis. However, the results by these commonsolutions are not intuitive for the users [3]. The flight data, e.g., the flight angles, positions and mAccordingly, it is a better way to recreate the flight trajectory by visualizing the flight data.

The visual simulation technology makes it possible. Flight Viz [4] produced by SimAuthor

Company could playback the flight trajectory in 3D visual effects, but its cost is very high. The3D Flight Simulation System EasyFlight developed by China Academy of Civil Aviation Science

and Technology is a professional aeronautic platform [5]. Its mainly used in flight simulation ofmajor accidents, but rarely in common flight trajectory recreation. Yong Tang [6] presented a

solution for 3D flight trajectory and 6-DOF flight simulation based on Google Earth [7]. But theresearch result relies much on the server of Google Earth, thus the users may concern about the

security and the cost.


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142 Computer Science & Information Technology (CS & IT)

From the point of view of the cost and security, secondary development on open-source platformis a better choice. In this paper, ossimPlanet [8] is taken as the development platform. It is an

accurate 3D global geo-spatial viewer that is built on the OSSIM [9], OpenSceneGraph [10], andTrolltech QT[11] open source software libraries [12]. It could provide accurate 3D globalvisualization and collaboration [13], and has the following three advantages: (1) Its open-source.

It costs less than platform, e.g., Google Earth. Especially, we can realize more customized

functions and ensure its security. (2) Its built on OSSIM, which has a powerful suite of

geospatial libraries and applications to process imagery, maps, terrain, and vector data [9]. Thispaper focuses on the flight trajectory of aerial mission, which includes a lot of aerial photographs.

Thus, OSSIM can provide strong support on image processing. (3) any other flight parameterscould describe the spatial status of flight.

Its written in C++ and thus has higher performance than the platforms written in other languages,such as World Wind written in C#.

In this paper, a flight trajectory recreation and playback system of aerial mission will beimplemented based on ossimPlanet. The system would recreate and playback the trajectory on 3D

global, thus it will be more intuitive. The development on ossimPlanet ensures the security in alow cost and high performance. This paper is organized as follows. In Section II, the requirementanalysis of the whole system is presented. The key problems and the corresponding solutions are

given in Section III. The system realization is introduced in Section IV. The simulation results areshown in Section V. The conclusions are summarized in Section VI.

2. REQUIREMENTANALYSIS

The following formatting rules must be followed strictly. This (.doc) document may be used as a

template for papers prepared using Microsoft Word. Papers not conforming to these requirementsmay not be published in the conference proceedings.

The system functions are shown in Fig.1, and their detailed descriptions are given below.

Choose flight. Users are allowed to choose their interested flight, that is, to fix the localpath where the aerial photographs and corresponding configuration files are located. Then

these files would be read in, and the statuses of the plane are stored after the necessary

processing on these input files.

Observe photographs. Users are allowed to observe the input photographs. Thesephotographs would be pasted on their correct positions which are set in the configuration

files.

Observe trajectory. Users are allowed to observe the flight trajectory on the 3D global ofossimPlanet. Both the input flight trajectory points and the interpolated trajectory points

are marked on the 3D global.

Observe simulation. Users could follow the planes eye point to view the flight trajectorydynamically.


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Computer Science & Information Technology (CS & IT) 143

Fig. 1. Use case diagram.

3. KEYPROBLEMS

There are three key problems for the system realization. (1) Data processing. The input dataincludes the aerial photographs and configuration files. Every aerial photograph has a

corresponding configuration file in which the flight data is included, e.g., the flight statuses, flight

positions, pilots operations, etc. The required flight data will be taken for interpolation. (2) Datadisplay. It is to display the aerial photographs and mark flight trajectory points on the 3D global

of ossimPlanet. (3) Flight trajectory playback. It is to playback the flight trajectory on the 3Dglobal of ossimPlanet.

3.1. Data Processing

Without loss of generality, we make following assumptions on the motion of plane: (1) Its rigidbody motion. (2) The translation is with the centroid and the rotation is around the centroid.

To describe the motion clearly, we should take proper flight data from the configuration files.

Generally, 6 degree-offreedom (DOF), i.e., 3 position coordinates (longitude, latitude and height)

and 3 posture angles (heading angle, pitch angle and roll angle), is always used [6]. The postureangles are shown in Fig.2.

Fig. 2. The heading, roll and pitch angle of plane [14].


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After we get the flight trajectory points contained the 6 DOF parameters, its necessary to smooththe flight trajectory by interpolation. The interpolation on the position coordinates and posture

angles will be done respectively. Since its shown that the unstable heights may result in flightcollision [15], the height is assumed invariable in position coordinates and not interpolated. DeBoor's algorithm [16] will be used to interpolate the longitude and latitude. In the posture angles,

the heading angle is changed with the stress of plane [17] and always very small. The changes of

pitch angle in real aerial mission are generally less than 5 degrees and roll angle is always 0

degree [18]. In this paper, we use linear interpolation for the posture angles smoothing.

3.2. Data Display

3.2.1. Photograph Display

To display the photographs on the 3D global of ossimPlanet, the corresponding geometry files for

photographs are required. A geometry file instance is given in Fig. 3.In which the projection type,

datum, longitude, latitude and some other geographic parameters are set.

type: ossimEquDistCylProjection

origin_latitude:0.0central_meridian: 0.0pixel_scale_units: degrees

pixel_scale_xy: ( .133, .133 )

datum: WGE

tie_point_units: degrees

tie_point_xy: (-180.0, 90.0)

pixel_type: area

Fig. 3. Geometry file instance.

In Fig. 3, the type defines the projection of the photograph, and the default projection of

ossimPlanet is cylindrical equidistant projection [19]. The origin_latitude and thecentral_meridian are always 0 degree. The pixel_scale_xy is the actual scale of every pixel of the

photograph and its unit is defined in the pixel_scale_units. The tie_point_xy is the coordinate ofthe photograph as (longitude, latitude) and its unit is defined in tie_point_units.

After the photographs and configuration files are read in, the corresponding geometry files arecreated according to the configuration files. Then by using ossimPlanets API, the photographs

could be displayed on the 3D global.

3.2.2. Flight Trajectory Display

Keyhole Markup Language (KML) [20] is a Markup Language to describe and store geographical

information, such as point, line, surface, three-dimensional models, etc. A KML file instance isgiven in Fig.4.

Generally, a KML file includes 3 parts: (1) XML Header; (2) The definition of KML namespace;(3) The object of geographical indication [21]. In Fig.4, indicates a style may be used for

objects and indicates a place mark. The KML file in Fig.4 indicates a point at

(121.48844, 53.332649, 0), and it will be shown as an icon whose hyperlink is given in thereferenced link.


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reference link

#style60

121.48844,53.332649,0

Fig. 4. KML file example.

A KML file is created for the input trajectory points and interpolated trajectory points. Then byusing ossimPlanets API, the KML file could be loaded and thus the trajectory points could bemarked on the 3D global.

3.3. Flight Trajectory Playback

To playback the flight trajectory, its necessary to have the knowledge of the 3D world of

ossimPlanet. (1) Coordinate Systems and Transformations. In the 3D world, the basic work is toconfirm the coordinate systems and find out the coordinate transformations. (2) ViewTransformation. To playback flight trajectory is to change the eye point with the flight status.

Thus the view transformation is important. (3) Rendering theory of ossimPlanet. The actualdevelopment work should be based on the rendering theory of ossimPlanet.

3.3.1. Coordinate Systems and Transformations

The Geographical Coordinate System, World Coordinate System and Local Coordinate System

are briefly introduced as follows:

a) Geographical Coordinate System. In this coordinate system, each point is determined by itslongitude, latitude and the height above a WGS-84 reference ellipsoid [22].

b) World Coordinate System.The world coordinate of ossimPlanet is Earth Centered EarthFixed (ECEF) [23], as the XYZ coordinate system shown in Fig.5.

c) Local Coordinate System.The local space reference (LSR) system of ossimPlanet is as UVWcoordinate system shown in Fig.5.


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Fig. 5. Coordinate systems of ossimPlanet[24].( is longitude ,is latitude and h is the height )

Both the Geographical Coordinate and the Local Coordinate could be converted into the World

Coordinate as follows [24].

a) From Geographical Coordinate to ECEF( )coscosX h= +

( )cossin Y h= + (1)2[(1- ) ]sinZ e h= +

b) From LSR to ECEF0 0 0 0 0 0- sin - sin cos cos cosX X U V W= +

0 0 0 0 0 0cos - sin sin cos sin Y Y U V W = + + (2)

0 0 0cos sinZ Z V W= + + ,

where is normal vector of latitude and its value is

2 2 0.5

/ (1- sin )a e=

, h is the height above

the surface of ellipsoid, e is eccentricity and2 2 2 2 2( - ) / 2 -e a b a f f = = , is latitude and is

longitude, a is semi-major axis, b is semi-short axis and f is flattening.

3.3.2. View transformation

From the general process of 3D graphics display [25], we can easily convert the World

Coordinate to the View Coordinate as follows,

VM PM WMViewCoord WorldCoord * * *= , (3)

where VM is the view matrix, PM is the projection matrix and WM is the window matrix.

In ossimPlanet, PM and WM in (3) are fixed. Therefore, VM should be calculated for the viewtransformation. That is to place the eye point of ossimPlanet on the proper position in proper

posture. The position of eye point is determined by the position of the plane given in the

configuration files. Then we can convert the position coordinate in the Geographic Coordinate

System GeoEye(l,l,h) to that in the World Coordinate System 0 0 0WorldEye(x ,y , z ) as in (1).

From the posture angle, we can get the rotation matrix of the eye point:


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z y xRotateMatrix R (h) * R (p) * R (r)= , (4)

where h is heading angle, p is pitch angle and r is roll angle. zR (h)

yR (p) and xR (r) are the

corresponding rotation matrixes [25].

Since RotateMatrix is in the Local Coordinate System, we should convert it to the WorldCoordinate System as in (2) and have the rotation matrix of the eye point in LSR,

RotationLsrMatrix = RotateMatrix *LsrMatrix , (5)

then, VM is as follows:

ViewMatrix = RotationLsrMatrix* WorldEye , (6)

3.3.3. Rendering Theory of ossimPlanet

The rendering circle [26] of ossimPlanet is to loop the frame() before the scene is finished. Every

frame has the following three traversals:

a) Event Traversal. This part is implemented in eventTraversal(), where the different kinds of

events are handled. The events include the mouse events, keyboard events, windows, callbacks ofcameras, etc.

c) Updating Traversal. This part is implemented in updateTraversal(), where the updatingcallbacks are traversed and executed .

d) Rendering Traversal. This part is implemented in renderingTraversal(), where the renderingwork such as the Cull and the Draw are done.

The basic rendering progress in ossimPlanet is described below. (1) The events from GUI or the

scene are caught and handled in Event Traversal. The corresponding scene parameters are alsocalculated. (2)The scene parameters calculated by the Event Traversal are updated in UpdatingTraversal. (3)The scene parameters updated in Updating Traversal would be shown by Rendering

Traversal. Thus, the scene would change with the events through the cooperation of the 3traversals.

In ossimPlanet, the rendering circle is finished in a component called Viewer. Its shown in Fig. 6that the Viewer includes Manipulator, GUI Event Handler, Scene and Camera. The Manipulator

is an instance for roaming in the scene of the Viewer. All of the events from the GUI or the scene

will be collected in the Manipulator. And these event messages will be translated to and finally

handled in Navigator. In Navigator, the calculations of scene parameters of Event Traversal arecompleted.

To implement playback of flight trajectory in ossimPlanet, we should add our own event handlersin Event Traversal. And the handlers would handle customized events and calculate the scene

parameters as we design. The rest work could be then done by the other 2 traversals.


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Fig. 6. Viewer of ossimPlanet.

4. SYSTEMREALIZATION

Based on the analysis in Section III, the system realization is mainly to overwrite the Manipulator

and Navigator of ossimPlanet. The user interactions are through the GUI (ossimPlanet

QtMainWindow) and the corresponding event handlers are added in Navigator following thetheory of Event Traversal. To store the information of flight trajectory, data structures are

designed.

4.1. Component Design

The component diagram of the whole system is shown in Fig.7 and the corresponding description

is summarized below.

GUI (ossimPlanetQtMainWindow) provides 3 interfaces for user interactions.

on_viewStartInputtingPath_triggered() is for inputting the interested flight of aerial mission,

on_flieOpenKml_triggered() is for displaying the flight trajectory andon_viewShowThePath_triggered() is for simulating the flight trajectory playback. After users

operations, GUI will translate event messages to the Navigator which is bridged by theManipulator. Then, Navigator will handle these events.

Fig. 7. Component diagram.


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4.3. Storage of Interested Flight

After users input the interested flight from GUI, the on_viewStartInputtingPath_triggered() is

triggered. The cooperation diagram is shown in Fig.9.

Fig. 9. Cooperation of the components after inputting interested flight.

The message translation and cooperation are summarized below.

Users fix the path of the aerial photographs and configuration files. Then the point offlight trajectory is stored as PathPoint and the input trajectory points as an array of

PathPoint. The geometry files are also created.

createLayer() is invoked, and the texture layers corresponding to the photographs arecreated.

addTop() is invoked to load these layers. The actual locations of the photographs aredefined in the corresponding geometry files so that the photographs are displayed in thecorrect positions.

GUI translates the event messages to the Navigator through the Manipulator.

In the Navigator, the input flight trajectory points are interpolated and the results arestored as ossimPlanetAnimationPath.

4.4. Display of Flight Trajectory

After users choose to display the flight trajectory from GUI, the on_flieOpenKml_triggered() is

triggered. The cooperation diagram is shown in Fig. 10, and the message translation and

cooperation are summarized below.

The users option is translated to the Navigator through the Manipulator.

In the Navigator, the CreateKmlFilePath() is invoked to create a KML file.

Traverse the input trajectory points and export them into the KML file.

Traverse the interpolated trajectory points and export them into the KML file.

The addkml() in ossimPlanetKmlLayer is invoked to create a corresponding KML layer

on ossimPlanet for display.


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Fig. 10. Cooperation of the components after choosing to display trajectory.

4.5. Playback of Flight trajectory

After users choose to playback the flight trajectory, on_viewShowThePath_triggered() istriggered. The cooperation diagram is shown in Fig.10. The message translation and cooperation

are summarized blow.

The users option is translated to the Navigator through the Manipulator.

In the Navigator, the showPath() is invoked. Current rendering mode is set as thesimulation mode.

The rest work is done along with the Event Traversal. In every frame, the scene

parameters are calculated in update(). And the calculation is done according to theControlPoint in the map of ossimPlanetAnimationPath .

Loop the third step with the refresh of ossimPlanet to playback the flight trajectory

dynamically.


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Fig. 11. Cooperation of thecomponents after choosing to playback the flight trajectory.

5. SIMULATION RESULTS

The simulation is done on the ossimPlanet 1.8.4. The interested flight data includes tenphotographs and their configuration files. The 10 red-dotted points are the input flight trajectory

points as shown in Fig.12 and the corresponding photograph is pasted as shown in Fig.13. The

green marks are the interpolated flight trajectory points.

Fig. 12. Marks of flight trajectory.

Fig. 13. Playback of flight trajectory.


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During playback of flight trajectory, the eye point changes along the flight trajectory. As shownin Fig.13, users could view the photographs and the trajectory marks on the 3D global

dynamically. The eye point will change with the plane when the ossimPlanet refreshes its scene.

6. CONCLUSIONS

In this paper, flight trajectory recreation and playback system of aerial mission is implementedbased on open-source 3D global platform ossimPlanet. Users can choose their interested flight

of aerial mission. Then the aerial photographs would be displayed on the proper geographic

positions of ossimPlanet. The flight trajectory also would be recreated and marked. In addition,

the playback of the flight trajectory is simulated on ossimPlanet. These functions allow users toanalyze their interested flight in a more institutive way.

The development on open-source platform ensures the security of system in a low cost and highperformance. Especially, it allows developers to implement more customized functions. During

the development, APIs of ossimPlanet about loading images, loading KML files and renderingframe are overwritten. This paper provides a general method for the development on ossimPlanetwith its rendering theory.

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Authors

Wu Wu is a graduate student for master at the Research Center for Natural Computing

and Software, College of Computer Science and Technology, Beijing Nor-mal University.

Her research interests include software engineering and info-rmation systems,3D GIS.Heremail is [email protected];

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